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RF Ion Sources
The Oxford Applied Research RF ion sources are employed in applications where ion-beam etching, sputter deposition or assisted deposition are required with minimal contamination. The inductively-coupled discharge requires no hot cathode and, with the exception of the extraction grids, takes place entirely within an ultra-pure ceramic discharge zone. This configuration lends itself to operation with reactive gases, such as oxygen, hydrogen or nitrogen without the accelerated degradation of the discharge zone as observed in filament-driven ion sources.
Beam profile
The sources can be equipped with a variety of grids, to tailor the beam profile to a particular application. For example, convex grids can be used for irradiation of large areas with high uniformity. Concave grids can be employed to focus the beam for applications where very high current-density is required, such as sputter deposition.

Reactive gases
One of the primary advantages of RF sources over filament-driven DC ion sources is the resistance they demonstrate to attack by reactive gases. This allows operation with pure oxygen, for example, in ion-beam assisted deposition of oxide films. With many of today’s optical filters consisting of oxide multilayers, RF ion sources are an invaluable component of ion-beam deposition systems.

High current-density
Exceptionally high current density can be achieved using our RF ion sources. The graph to the right shows the 50mm RF50 source operating on pure oxygen. A current density greater than 6mA/cm2 can readily be achieved at high energy while, at low energy, the current density is still in excess of 1.5 mA/cm2.

Low maintenance
Production processes require high uptime and correspondingly low maintenance. RF ion sources use no hot cathode in the discharge zone, requiring no regular replacement of filaments. In addition, the extraction efficiency of ion current is extremely high, resulting in low sputter-damage to the grids. As a result grids need only be replaced very infrequently, even in reactive environments.

Grid Materials
Grids can be supplied in a variety of materials to suit particular applications. For the lowest sputter-damage of the grids during operation, for example, carbon should be employed, while molybdenum grids are usually used for prolonged operation with pure oxygen. Grids can be shaped to produce focused or divergent beams to facilitate sputter deposition and large-area coverage respectively.

Beam Neutralisation
Ion beam impingement on insulating surfaces will lead to a rapid build up of charge. This can significantly affect the characteristics of the ion beam profile and consequently degrade the deposition process. The solution to this problem lies in injecting electrons into the ion beam in sufficient number to completely neutralise it. This can be accomplished by a number of different methods according to budget and application. We offer plasma bridge neutraliser and filament-based electron injection sources. Both can be supplied for prolonged use with reactive gases.

Source Construction
Sources are available in flange mounted or internal mount versions. Oxford Applied Research has a long tradition of supplying UHV instruments. The discipline imposed by operation in ultra-low contamination environments has been inherited in the design of our RF ion sources. All flange-mounted sources are true-UHV, allowing bakeout at 200oC if desired, while internal-mount sources are manufactured predominantly from UHV-compatible materials. In addition, the discharge-zone is enveloped by a water cooling jacket, relieving the radiation load on the chamber. This construction ensures that contamination and substrate-heating during operation is kept to a minimum.

Power supplies
All RF and DC power supplies are provided for immediate operation of the sources. The control can be configured for simple, manual control, or for full PC-based automation.

RF ion source specifications
Article: "Ion beam mirrors for EUV lithography"